The present invention relates to the field of thermoplastic elastomer compounds useful in molding of shoe soles, alloys and adhesives.
Highly branched block copolymers, sometimes called star-block copolymers, are old in the art of anionic polymerization. These star-block copolymers are prepared by first forming linear block polymers having active lithium atom on one end of the polymer chain. These active linear polymer chains are then coupled by the addition of a polyfunctional compound having at least three reactive sites capable of reacting with the carbon to lithium bond on the polymer chains to add the polymer chain into the functional groups of the compound.
Zelinski, U.S. Pat. No. 3,280,084, polymerized butadiene with butyllithium initiator to form B-Li blocks (where B is polybutadiene) which when coupled with 0.02 to 1 part by weight per 100 parts of monomers of divinylbenzene gave star-block copolymers having polydivinylbenzene nuclei and several identical arms of polybutadiene branching therefrom. The arms can also be either random or block copolymers of styrene and butadiene (from A-B-Li blocks, where A is polystyrene segment) where the diene is the major component.
Zelinski, U.S. Pat. No. 3,281,383, teaches similar star-block copolymers to those in U.S. Pat. No. 3,280,084, except that coupling agents such as polyepoxy compounds, polyacids, polyaldehydes, etc., are used.
Haefele et al, U.S. Pat. No. 3,485,787, produces elastomeric compositions by blending mineral oils with thermoplastic linear triblock copolymers by milling the ingredients.
Childers, U.S. Pat. No. 3,637,554, prepares rubbery star-block copolymers having nuclei formed from polyepoxides, polyisocyanates, polyimines, etc., and identical arms from B-Li and A-B-Li.
Fetters et al, U.S. Pat. No. 3,985,830, discloses a product having a nucleus of more than one molecule of m-divinylbenzene and at least three polymeric arms, each being a block copolymer of conjugated diene and monovinyl aromatic monomers wherein said conjugated diene block is linked to said nucleus.
Himes, U.S. Pat. No. 4,107,124, teaches compositions comprising star-block copolymers, polystyrenes, mineral oil, and a finely divided filler for use in shoe sole compositions. The ingredients are blended in an extruder, a Banbury mixer or by dry-blending.
Hansen, U.S. Pat. No. 4,141,876, produces adhesive compositions by melt-blending a hydrogenated star-block copolymer with mineral oil, a polyphenylene ether resin and a tackifying resin.
The thermoplastic elastomers are prepared by polymerization of monomers in inert solvent. The product elastomers are normally separated from the solvent by steamstripping the unreacted monomers, coagulating the polymer with water and separating the wet polymer as a crumb. The crumb is deashed, dried of solvent and water and sold loose or converted to pellets by extrusion or powder by grinding.
The neat elastomer, as crumb, pellets or powder must then be blended with the ingredients necessary to form either oil-extended elastomer or shoe sole compound. A typical shoe sole compound comprises for each 100 parts by weight of neat elastomer, 50-200 parts extender oils, 25-150 parts reinforcing fillers or pigments, 50-200 parts polystyrene materials and 0.1-2.0 parts stabilizers.
The blending process requires that the neat elastomer be isolated from its polymerization medium and then remelted during the blending to insure good mixing of the ingredients of the shoe sole formulation or compound.